The present invention relates to an optical attenuator, and in particular, to variable optical attenuator that may utilize an alignment beam for control of the attenuation.
Over the past several decades, the telecommunications industry has exploded, and the incorporation of optical fiber into this industry is revolutionizing the way information is transmitted. Communication systems which use optical fiber as the transmission media offer some significant advantages over traditional wire-based systems, such as higher bandwidths and transmission rates, lower transmission losses, lower implementation costs, and greater electrical isolation.
Optical components utilized in these optical fiber communications systems typically require an ability to operate over a wide range of power levels. Devices, such as optical attenuators, have been developed to control optical signal power attenuation. Several types of optical attenuators have been developed, but these systems and devices have several drawbacks.
For example, one system attempts to provide optical attenuator by varying the orientation between a pair of optical fibers. In this type of system, one fiber is maintained in a fixed position while the other fiber is mounted on a moveable surface so that its terminal end can be axially or angularly moved relative to the fixed fiber. In these types of systems, signal attenuation is described as being accomplished by moving one fiber relative to another, causing an imperfect transmission between the fibers.
Other systems utilize a variety of different types of signal blocking devices in an attempt to provide optical signal attenuation. One system, for example, describes an ability to provide signal attenuation by moving a light blocking member that is disposed between two optical fibers. These signal blocking systems include the utilization of optical shutters that are controlled by thermal actuators or other types of micro electromechanical systems (MEMS) devices.
Despite the problems inherent to the optical attenuators currently available, single mode (SM) fiber, with its virtually unlimited bandwidth, has slowly become the standard in the telecommunication industry. Since the diameter of the core in a SM fiber is approximately ten (10) microns, the optical attenuators which use crude drive mechanisms are incapable of precise signal attenuation.
In view of the foregoing, a present need exists for an optical attenuator that can provide optical signal attenuation over a full optical power range. Additional need exists for precise control over the optical attenuation, allowing for the transmitted optical power to be dynamically altered as may be required by a specific application.
The variable optical attenuator of the present invention may be configured to generate a communication beam at an optical input fiber, as well as an associated alignment beam at a beam generating element. The alignment beam may be received by a sensor that can provide a relative location of the alignment beam with respect to the sensor. The communication beam may then be positioned so that a desired percentage of the communication beam enters an output fiber, where the positioning of the communication beam utilizes information, such as the offset from the location of said alignment beam.
In accordance with another aspect of the present invention, the positioning of the communication beam is performed by directing the communication beam to a MEMS device, and then positioning the MEMS device so that the desired percentage of the communication beam enters the output fiber.
In another aspect of the present invention, positioning is performed by directing the communication beam to a first MEMS device which may be positioned so that the communication beam is reflected from a surface and is redirected to a second MEMS device. The second MEMS device may be positioned so that the desired percentage of the communication beam enters the output fiber.
In still yet another aspect of the present invention, the alignment beam may be repeatedly received to provide updated locations of the alignment beam. Then the communication beam may be repositioned as necessary to reflect any change in location of the alignment beam to maintain the desired percentage of the communication beam that enters the output fiber.
In another aspect of the present invention, the desired percentage of the communication beam that enters the output fiber may be repeatedly determined to ascertain whether the desired percentage has changed. As such, the communication beam may be repositioned as necessary to reflect any change in the desired percentage of the communication beam that enters the output fiber.
In yet another aspect of the present invention, the communication beam may be positioned at about a center of a core in the output fiber so that about all of the communication beam enters the output fiber. Alternatively, the communication beam may be positioned at an offset from a center of a core in the output fiber so only a portion of the communication beam enters the output fiber.
In still yet another aspect of the present invention, each of a plurality of locations on the sensor corresponds to a particular offset that the communication beam enters the output fiber.
In yet another aspect of the present invention, the communication beam and alignment beam may be generated at a beam generation element, and then proceed along paths that are either substantially parallel, parallel, converging, or coaxial.
In accordance with another aspect of the present invention, the sensor may comprise a sensor, such as a position sensitive diode (PSD), a charge coupled device (CCD), or a light sensitive CMOS sensor.
In another aspect of the present invention, the alignment beam may be generated by a light source, such as a light emitting diode (LED), an optical fiber, a laser, or a vertical cavity surface emitting laser (VCSEL).
In still yet another aspect of the present invention, lenslets may be provided at the beam generating element and/or at the beam receiving element to provide collimating and focusing as may be necessary.
In yet another aspect of the present invention, optical beam attenuation may be provided by using a single, or even multiple reflecting devices. In this configuration, a beam generating element may comprise an optical input fiber and a first lenslet. A beam receiving element may also be provided, which may comprise an optical output fiber and a second lenslet. Typically, a communication beam is generated at the optical input fiber and then collimated by the first lenslet. The collimated communication beam may then be directed to a MEMS device, which may reflect the beam so that it can pass through the focusing lenslet. The focused communication beam may then be positioned so that a desired percentage of the communication beam enters an output fiber. The communication beam positioning may be provided by one or more of the MEMS devices using, for example, the known relative locations of the input fiber and the output fiber.